During 2018, coal supplied 13.1% of all the energy consumed in the U.S., while renewables supplied a combined total of 11.2%. This includes hydroelectric (2.7%), wind (2.5%), biofuels (2.3%), wood (2.1%), solar (0.9%), biowaste (0.5%), and geothermal (0.2%). Per the Department of Energy: "While coal used to be a dirty fuel to burn, technology advances have helped to greatly improve air quality, especially in the last 20 years." In the U.S. from 1990 through 2017, sulfur dioxide emissions per Btu of coal-generated energy decreased by 91%, and nitrogen oxides emissions decreased by 83%.